Well this is a bit of a thread dive, but ok, I'm game.
Towing a car across the country on a trailer is just plain nuts.
1) Petrol prices are extortionate, and your consumption will go through the roof.
2) You're going to put an incredible strain on your gearbox and cooling system. And if you think the petrol prices are bad, wait til you try and organise repairs.
3) I have certainly broken the law with a car-trailer. In fact most car-trailers are fundamentally illegal. Most have over-rider Brakes, and in WA that limits you to 2T GTM. Load up anything heavier than a Getz and you're probably over the limit
But with big loads (eg towing one AU with my other) I've kept the speed to around 80, and that only on the freeway. Plus if a cop did pull me over, I'm only a $50 tow from home. I don't fancy being stuck in the middle of the Nullabor, and being told you have to unload your new car and leave it behind. And who's to say that what's acceptable in WA, doesn't get you a reaming in another state?
4) If you run over a bunch of stones with the tow car, have a guess where they're likely to end up.
5) Most insurance policies will cover you for towing a garden trailer. I'm not sure that either policy would cover you if you flip a trailer with your new car on it.
6) As to your other question, if it costs say $1k for CEVA depot to depot, then nobody in their right mind is going to pay some rando (ie you) even $500 to try and move their pride and joy on said rando's mate's trailer.
7) I bought my TTG from Adelaide, and saved at least $6k on the purchase price (at that time Perth was still plagued with CUBs). I did the maths, and CEVA was cheaper than fly & drive.
8) If you're not prepared to buy an interstate car without a personal inspection, then I can't really understand what your "plan" is?
You're going to hunt for the car you want, then ask them to hold on, whilst you phaff about trying to find a backload for your trip and then drive across the continent?
And then what? What if your personal inspection reveals the hidden flaw you're so worried about? You try to arrange another rando load for your trip home?